JP7163107B2 - ink - Google Patents

Description

Embodiments of the present invention relate to inks.

2. Description of the Related Art In recent years, from the viewpoint of environmental protection, economic efficiency, etc., there has been a demand for a reduction in the amount of recording media such as paper. Additive reverse thermochromic ink compositions that can be rendered substantially colorless by interaction or contact with a decolorant are known to meet such demands. Specifically, additive reverse thermochromic ink compositions are known that include a color-changing dye, a color activator, a decolorant, and a wax to chemically separate the color-changing dye and color activator from the decolorant. It is (Patent Document 1)

Japanese Patent Publication No. 2015-509121

The problem to be solved by the present invention is to provide an ink excellent in color developability and color erasability.

According to an embodiment, the color former comprises a color former, a developer that develops the color of the color former, a non-aqueous solvent, and a decolorant , and the decolorant is insoluble in the non-aqueous solvent. and includes only those that decolorize the color former by heating, the decolorant is selected from the group consisting of xylitol, D-sorbitol, D-mannitol and trimethylolpropane, and the developer is An ink is provided that is a silicon oxide .

1 is a schematic diagram showing an example of an image forming apparatus to which ink according to one embodiment can be applied; FIG.

Embodiments will be described below.

1. Structure of Ink The ink according to one embodiment includes a color former, a color developer that develops the color former, a non-aqueous solvent, and a non-aqueous solvent that is insoluble in the non-aqueous solvent. and a decolorizing agent.
Each component will be described below.

<Coloring compound>
The color former is a substance that develops color by reacting with a developer described below. The color former is preferably an electron-donating substance.
As the color former, for example, leuco dyes, specifically electron-donating organic substances such as leuco auramines, rhodamine B-lactams, indolines, spiropyrans, and fluorans can be used.

More specifically, for example, the following dyes can be used.
Crystal violet lactone (CVL), malachite green lactone, 2-anilino-6-(N-cyclohexyl-N-methylamino)-3-methylfluorane, 2-anilino-3-methyl-6-(N-methyl-N -propylamino)fluorane, 3-[4-(4-phenylaminophenyl)aminophenyl]amino-6-methyl-7-chlorofluorane, 2-anilino-6-(N-methyl-N-isobutylamino)- 3-methylfluorane, 2-anilino-6-(dibutylamino)-3-methylfluorane, 3-chloro-6-(cyclohexylamino)fluorane, 2-chloro-6-(diethylamino)fluorane, 7-(N ,N-dibenzylamino)-3-(N,N-diethylamino)fluorane, 3,6-Bis(diethylamino)fluorane-γ-(4′-nitro)anilinolactam, 3-diethylaminobenzo[a]-fluorane , 3-diethylamino-6-methyl-7-aminofluorane, 3-diethylamino-7-xyridinofluorane, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methyl indol-3-yl)-4-azaphthalide, 3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide, 3-diethylamino-7-chloroanilinofluorane, 3-diethylamino-7,8-benzofluorane, 3,3-Bis(1-n-butyl-2-methylindol-3-yl)phthalide, 3,6-dimethylethoxyfluorane, 3-diethylamino-6 -Methoxy-7-aminofluorane, DEPM, ATP, ETAC, 2-(2-chloroanilino)-6-dibutylaminofluorane, crystal violet carbinol, malachite green carbinol, N-(2,3-dichlorophenyl) leuco Auramine, N-benzoyl auramine, rhodamine B lactam, N-acetyl auramine, N-phenyl auramine, 2-(phenyliminoethanedylidene)-3,3-dimethylindoline, N-3,3-trimethylindoline Rinobenzospiropyran, 8′-methoxy-N-3,3-trimethylindolinobenzospiropyran, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-6 -benzyloxyfluorane, 1,2-benz-6 -diethylaminofluorane, 3,6-di-p-toluidino-4,5-dimethylfluorane-phenylhydrazide-γ-lactam, and 3-amino-5-methylfluorane. can.

These can be used alone or in combination of two or more. By appropriately selecting the color former, various colored states can be obtained, so that it is also possible to express multiple colors.

The ink according to the embodiment preferably contains 5 to 50 parts by mass, more preferably 10 to 40 parts by mass, of the color former with respect to 100 parts by mass of the developer. .

<Developer>
A developer is a substance that causes a color former to develop a color. The developer is preferably an electron-accepting substance. According to one example, when the color former is bound to the surface of the developer, electrons are donated from the color former to the developer, and as a result, the color former develops color. Hereinafter, the particles in which the color-developing compound is colored by binding the color-developing agent and the color-developing compound are also referred to as color-developing particles.

As the color developer, it is more preferable to use, for example, silicon oxide. As silicon oxide, for example, silica, particularly preferably activated silica, can be used. Here, "active silica" means highly reactive silica due to its large surface area. Activated silica has excellent thermal stability and is suitable for making particles smaller. Since this makes it possible to reduce the size of the color developing particles, the use of active silica as a color developer is advantageous in forming high-definition images. Moreover, since such a color developer has a high affinity for hydrophilic substances, it is particularly excellent in reactivity with the decolorizing agent described below.

As the color developer, it is preferable to use a silicon oxide having a specific surface area according to the Brunauer, Emmett and Teller (BET) method in the range of 50 to 500 m ² /g, preferably in the range of 100 to 400 m ² /g. It is more preferred to use a silicon oxide in

Also, the average primary particle size of the developer is preferably in the range of 5 nm to 100 nm, more preferably in the range of 7 nm to 20 nm. Incidentally, the average primary particle size described here is calculated from the BET value. Also, the term "average particle size" described below means an average primary particle size, and this average primary particle size means a value obtained by a dynamic light scattering method.

Specifically, as the developer, for example, AEROSIL (registered trademark) 300 (Aerosil) and CAB-O-SIL (registered trademark) fumed silica HS-5 (Cabot Corporation) can be used.

Color-forming particles contain a developer and a color-forming compound directly bound to the surface of the developer. The average particle size of the coloring particles is preferably 10 μm or less, more preferably 1 μm or less. When the coloring particles are used in an inkjet ink, the average particle size of the coloring particles is preferably in the range of 10 nm to 1000 nm, more preferably in the range of 50 nm to 200 nm.
The ink according to the embodiment preferably contains coloring particles in the range of 1 to 50% by mass, and more preferably in the range of 5 to 30% by mass.

<Non-aqueous solvent>
A non-aqueous solvent is a fluid solvent other than water. Non-aqueous solvents are liquid at 25°C. The non-aqueous solvent is a solvent in which the decoloring agent described later is insoluble. By using a solvent in which the decoloring agent is insoluble as the non-aqueous solvent, it is possible to prevent the decoloring agent from decolorizing the color former in the ink. The non-aqueous solvent may be a single component or a mixture.
Here, "insoluble" means that the decolorant has a solubility of 0.1% or less in a non-aqueous solvent at 25°C.

The non-aqueous solvent is preferably a non-polar solvent. As such a non-aqueous solvent, it is preferable to use, for example, liquid paraffin.
Here, "paraffin" is a general term for alkanes having 20 or more carbon atoms. And "liquid paraffin" is a substance defined in JIS K2231:1993 "liquid paraffin".

Further, more specifically, non-aqueous solvents include MORESCO WHITE (registered trademark) P-40 (MORESCO), liquid paraffin (Wako Pure Chemical Industries, Ltd.), castor oil (Wako Pure Chemical Industries, Ltd.), and Teclean. (registered trademark) N-16 (Shin Nippon Petrochemical Co., Ltd.) can be used.

The ink according to the embodiment more preferably contains a non-aqueous solvent within a range of 40 to 90% by mass.

<Decoloring agent>
The decolorant is insoluble in the above non-aqueous solvents. Also, the decolorizing agent has the property of decolorizing the above-described color former by heating.

The decolorant preferably has an average particle size of 10 µm or less, more preferably 1 µm or less at 25°C. Further, when the decolorant is used in an inkjet ink, the decolorant preferably has a particle shape with an average particle size in the range of 10 nm to 1000 nm, more preferably in the range of 50 nm to 500 nm. is doing. A decolorant having an average particle size within the range described above is highly dispersible in ink and is advantageous in exhibiting excellent decolorizing properties.

The decolorizing agent is preferably a polyhydric alcohol. That is, the decolorant preferably has two or more hydroxyl groups in its molecule, more preferably three or more hydroxyl groups in its molecule. Compared with alcohols having only one hydroxyl group in the molecule, polyhydric alcohols have a higher affinity for the surface of a color developer made of an electron-accepting substance such as silicon oxide. Therefore, the use of a polyhydric alcohol as a decolorizing agent is advantageous in obtaining an ink with excellent decolorizing properties.

As the polyhydric alcohol, it is more preferable to use a sugar alcohol. That is, the decolorizing agent is preferably a polyhydric alcohol that does not have a cyclic structure in its molecular structure. In other words, the decolorant is preferably a linear polyhydric alcohol. Linear polyhydric alcohols are superior to polyhydric alcohols having a cyclic structure in color development.

Examples of sugar alcohols that can be used include the following.
Thus, for example, xylitol, D-sorbitol, D-mannitol can be used.

Polyhydric alcohols other than sugar alcohols can also be used as the decolorizing agent. As such polyhydric alcohols, for example, the following can be used.
Thus, for example, trimethylolpropane can also be used.

The decolorizing agent preferably has a molecular weight in the range of 100 to 1,000, more preferably in the range of 100 to 500.
Also, the melting point of the decolorizing agent is preferably in the range of 40 to 250°C, more preferably in the range of 50 to 200°C. If the melting point of the decolorant is too low, the color former may decolor at room temperature. If the melting point of the decolorizing agent is too high, decoloring may become difficult.

The ink according to the embodiment preferably contains the color erasing agent in the range of 2 to 50% by mass, more preferably in the range of 5 to 30% by mass.

By using the decolorizing agent described above in combination with the other components described above, it is possible to obtain an ink excellent in color developing property and decoloring property by heating. The expected mechanism of color development and decoloration of ink will be described below. Here, as an example, the case where the color former is a leuco dye, the color developer is active silica, and the decolorant is a polyhydric alcohol will be described.

At room temperature, a leuco dye as a color former is bonded to the surface of active silica as a color developer to form color-developing particles. At this time, the polyhydric alcohol as the decolorizing agent is dispersed in the non-aqueous solvent in the form of particles separate from the coloring particles. As a result, the decolorizing agent does not decolorize the color-developing particles, and the color-developing compound develops color.
When the ink is supplied to a recording medium such as paper, the non-aqueous solvent volatilizes. When the ink layer thus obtained is heated, the polyhydric alcohol melts and reacts with the surface of the activated silica. That is, the leuco dye bound to the surface of the activated silica particles is replaced by the polyhydric alcohol. This reduces the leuco dye bound to the surface of the active silica and decolorizes the ink.

<Other additives>
The ink according to the embodiment may further contain additives in addition to the components described above. For example, it may further contain general-purpose auxiliaries such as stabilizers, thickeners and preservatives.

As described above, in the ink according to the embodiment, elements including color forming particles composed of a color forming compound and a color developer, and a granular color erasing agent are dispersed in a non-aqueous solvent. When the particle size distribution of such ink is measured, the average particle size of the ink is preferably 10 μm or less, more preferably 1 μm or less. Moreover, when such ink is used as an ink for inkjet, the average particle size of the ink is preferably in the range of 10 nm to 1000 nm, more preferably in the range of 50 nm to 500 nm.

2. Effect The ink described above is excellent in color developability and color erasability.
As a decoloring method, for example, a two-liquid process is also conceivable. That is, an image is formed with an ink containing a color former and a color developer and does not contain a decoloring agent. can be considered. In this case, there is no need to consider decolorization of the color former due to mixing of the color former and developer with the decolorant in the ink. When adopting such a two-liquid process, there are few restrictions on the combination of the color former and the color developer and decolorant. In this case, therefore, it is possible to achieve, for example, excellent coloring and erasing properties. However, in this two-liquid type process, in addition to the ink, a separate liquid containing a decolorant is required.
On the other hand, the ink according to the embodiment can achieve excellent color developability and color erasability even though it is not a two-liquid type ink.

Also, as a color erasable ink, a double capsule structure in which a color developer and a color former are encapsulated in a first capsule coating, and the capsule and the color erasing agent are encapsulated in a second capsule coating. The ink used is also conceivable. In this case, since the developer and color former and the decolorant are separated from each other by the first capsule coating, the ink can exhibit excellent color development properties. Moreover, when such a structure is adopted, since the color former, the developer, and the decoloring agent are encapsulated in the same capsule by the second capsule coating, the decoloring property is excellent. However, such a capsule structure is difficult to reduce to small particles. Therefore, it becomes difficult to form a high-definition image.

On the other hand, the ink according to the embodiment can exhibit excellent color developability and color erasability in spite of not adopting a capsule structure.
Furthermore, the ink according to the embodiment can be made into small particles because it does not employ a capsule structure. Therefore, the ink according to the embodiment is also capable of high-definition image formation.

3. Method for Producing Ink The ink according to one embodiment can be produced, for example, as follows.
First, coloring particles are prepared. Specifically, a color former and a developer are mixed together with a solvent and stirred. Here, as a solvent used for mixing, for example, acetone, tetrahydrofuran, etc. can be used. The solvent is then removed, for example using a rotary evaporator, to obtain the color former. Then, this coloring material is pulverized using, for example, a bead mill to obtain coloring particles.
The decolorant is also pulverized using, for example, a bead mill, in the same manner as the color-developing particles. The decolorizing agent may be pulverized at the same time as the coloring material is pulverized. That is, the coloring material and the decoloring agent may be mixed and the mixture may be pulverized.
Next, the coloring particles and decolorizing agent are added to the non-aqueous solvent and mixed.
The ink according to the embodiment can be obtained by the above method.

4. Usage Form of Ink The ink described above can be used, for example, in an image forming apparatus. An example of using the above ink in an image forming apparatus will be described with reference to FIG.

FIG. 1 is a schematic diagram showing an example of an image forming apparatus according to one embodiment.
The image forming apparatus shown in FIG. 1 is an inkjet printer 100 .
The inkjet printer 100 includes a housing provided with a paper discharge tray 118, a paper feed unit, a medium holding mechanism, an inkjet head 115, and an ink cartridge 116 provided in the housing.

The inkjet printer 100 includes a housing in which a paper output tray 118 is provided. Cassettes 101a and 101b, paper feed rollers 102 and 103, transport roller pairs 104 and 105, registration roller pair 106, transport belt 107, fan 119, negative pressure chamber 111, transport roller pairs 112, 113 and 114, An inkjet head 115, an ink cartridge 116, and a tube 117 are installed.

The ink cartridge 116 includes an ink cartridge body and the above-described ink contained in the ink cartridge body.

The cassettes 101a and 101b accommodate recording media P of different sizes. The paper supply roller 102 or 103 takes out the recording medium P corresponding to the size of the selected recording medium from the cassette 101a or 101b and conveys it to the conveying roller pairs 104 and 105 and the registration roller pair .

The transport belt 107 is tensioned by a driving roller 108 and two driven rollers 109 . Holes are provided at predetermined intervals on the surface of the transport belt 107 . A negative pressure chamber 111 connected to a fan 119 is installed inside the transport belt 107 to attract the recording medium P to the transport belt 107 . Conveying roller pairs 112 , 113 and 114 are installed downstream of the conveying belt 107 in the conveying direction.

The image forming operation of the inkjet printer 100 will be described below.
First, an image processing means (not shown) starts image processing for recording, generates an image signal corresponding to the image data, and generates a control signal for controlling the operation of various rollers, the negative pressure chamber 111, and the like. do.

The paper supply rollers 102 or 103 take out the recording medium P of the selected size one by one from the cassette 101a or 101b under the control of the image processing means, and convey them to the conveying roller pairs 104 and 105 and the registration roller pair 106. do. The registration roller pair 106 corrects the skew of the recording medium P and conveys the recording medium P at a predetermined timing.

The negative pressure chamber 111 sucks air through holes in the conveyor belt 107 . Accordingly, the recording medium P is conveyed to a position below the inkjet head 115 as the conveying belt 107 moves while being attracted to the conveying belt 107 .

The inkjet head 115 ejects the above ink in synchronization with the timing at which the recording medium P is conveyed under the control of the image processing means. As a result, an image is formed at a desired position on the recording medium P. FIG.
Thereafter, conveying roller pairs 112 , 113 and 114 discharge the recording medium P on which the image is formed to a paper discharge tray 118 .
An image is formed as described above.
Here, although heating in the drying process after the ink is discharged is not described, drying by heating may be performed as long as the temperature is lower than the melting point of the color erasing agent.

The image thus formed can be erased by heating. Here, "heating" means raising the temperature to a temperature equal to or higher than the melting point of the decolorant. The heating method is not particularly limited, but may be, for example, heating using a heating device such as a heater, or heating by friction.

Here, an inkjet image forming apparatus has been described as an example of the image forming apparatus, but the image forming apparatus is not limited to this. The image forming apparatus may be, for example, an image forming apparatus using a printing method such as screen printing, intaglio printing, and letterpress printing.

In addition, as one embodiment of the ink usage pattern, an example of use in an image forming apparatus has been described, but the usage pattern is not limited to this. Inks may be used, for example, in writing instruments.

Examples are described below.

(Ink preparation)
Example 1
Inks were prepared as follows.
First, 10 parts by mass of crystal violet lactone (Yamada Kagaku Co., hereinafter referred to as CVL) as a color former, 50 parts by mass of AEROSIL (registered trademark) 300 (Aerosil Co.) as a developer, and 800 Parts by mass of acetone were mixed in an eggplant-shaped flask and stirred. After that, the acetone was dried using a rotary evaporator and mixed with a mixer to obtain colored particles.

Next, 80 parts by mass of MORESCO WHITE (registered trademark) P-40 (MORESCO) as a non-aqueous solvent, 5 parts by mass of coloring particles, and 15 parts by mass of xylitol as a decolorizing agent were mixed. , and pulverized in a bead mill to prepare an ink. The obtained ink is designated as ink I1. Beads with a diameter of 0.5 mm were used in the bead mill.
Also, the average particle diameter of the fine particles contained in the ink was about 200 nm.

Example 2
An ink was prepared in the same manner as in Example 1, except that D-sorbitol was used as the decolorant. The obtained ink is designated as ink I2.

Example 3
An ink was prepared in the same manner as in Example 1, except that liquid paraffin (Wako Pure Chemical Industries; CAS. No. 8042-47-5) was used as the non-aqueous solvent. The obtained ink is designated as ink I3.

Example 4
An ink was prepared in the same manner as in Example 1, except that D-mannitol was used as the decolorant. The obtained ink is designated as ink I4.

example 5
An ink was prepared in the same manner as in Example 1, except that trimethylolpropane was used as the decolorant. The obtained ink is designated as ink I5.

Example 6
An ink was prepared in the same manner as in Example 1, except that castor oil (Wako Pure Chemical Industries, Ltd.) was used as the non-aqueous solvent. The obtained ink is designated as ink I6.

Example 7
An ink was prepared in the same manner as in Example 1, except that Teclean (registered trademark) N-16 (Shin Nippon Petrochemical Co., Ltd.) was used as the non-aqueous solvent. The resulting ink is designated as ink I7.

Comparative example 1
An ink was prepared in the same manner as in Example 1, except that pure water was used instead of the non-aqueous solvent. The obtained ink is designated as ink C1.

Comparative example 2
An ink was prepared in the same manner as in Example 1, except that ethanol was used as the decolorant. The obtained ink is called ink C2.

Comparative example 3
An ink was prepared in the same manner as in Example 1, except that N-nonanol was used as the decolorant. The resulting ink is designated as ink C3.

Comparative example 4
An ink was prepared in the same manner as in Example 1, except that 1,2-hexanediol was used as the decolorant. The resulting ink is designated as Ink C4.

Comparative example 5
An ink was prepared in the same manner as in Example 1, except that 1,6-hexanediol was used as the decolorant. The obtained ink is designated as ink C5.
The decolorant had a solubility of 0.1% or more in a non-aqueous solvent.

Comparative example 6
An ink was prepared in the same manner as in Example 1, except that Emulgen (registered trademark) 103 (Kao Corporation) was used as the decolorant. The resulting ink is designated as Ink C6.

(evaluation)
The obtained ink was evaluated as follows.
A hand coater (RK Print Coat Instruments) was used to form a coating film of ink I1, and after drying, the image density was measured by X-Rite eXact. Further, this was heated to 100° C., and the image density after heating was also measured.

The image densities of the inks I2 to I7 and the inks C1 to C6 were similarly measured. Table 1 shows the results.

As shown in Table 1, the images formed using the inks I1 to I7 exhibited excellent performance in terms of color developability after drying and color erasability after heating.
On the other hand, the images formed using the inks C1 and C3 to C6 had low color developability and almost no decolorization. This result is considered to be due to the use of a solvent-soluble material as the decolorant. When such a material is used, the decolorant decolorizes the color former even in a non-heated state. Therefore, no decoloring effect due to heating is observed.
Ink C2 had an image density of 0.15 immediately after application, but increased to 0.4 after drying. This result is due to phase separation in the ink from immediately after coating to completion of drying. Further, no change in image density was observed before and after heating. This is believed to be due to the loss of ethanol through evaporation during the drying process.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the scope of the invention. Further, each embodiment may be implemented in combination as appropriate, in which case the combined effect can be obtained. Furthermore, various inventions are included in the above embodiments, and various inventions can be extracted by combinations selected from a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiments, if the problem can be solved and effects can be obtained, the configuration with the constituent elements deleted can be extracted as an invention.
The following is an additional description of the invention described in the original claims.
[1]
a color former,
a developer that develops the color former, and
a non-aqueous solvent;
and a decolorant that is insoluble in the non-aqueous solvent and decolorizes the color former by heating.
[2]
Item 2. The ink according to item 1, wherein the developer is a silicon oxide.
[3]
Item 3. The ink according to item 1 or 2, wherein the decolorizing agent is a polyhydric alcohol.
[4]
Item 4. The ink according to item 3, wherein the decolorizing agent is a sugar alcohol.
[5]
Item 5. The ink according to any one of Items 1 to 4, wherein the non-aqueous solvent is liquid paraffin.

DESCRIPTION OF SYMBOLS 100... Inkjet printer 101a... Cassette 101b... Cassette 102... Paper supply roller 103... Paper supply roller 104... Conveying roller pair 105... Conveying roller pair 106... Registration roller pair 107... Conveying belt 108... Driving roller 109 Driven roller 111 Negative pressure chamber 112 Conveying roller pair 113 Conveying roller pair 114 Conveying roller pair 115 Inkjet head 116 Ink cartridge 117 Tube 118 Paper discharge tray, 119... fan.

Claims (2)

a color former,
a developer that develops the color former, and
a non-aqueous solvent;
a decolorizing agent ;
The decolorizing agent includes only those that are insoluble in the non-aqueous solvent and decolorize the color former by heating,
the decolorizing agent is selected from the group consisting of xylitol, D-sorbitol, D-mannitol and trimethylolpropane;
The ink wherein the developer is silicon oxide . The ink according to claim 1 , wherein the non-aqueous solvent is liquid paraffin.

Images